A vehicle is obligated to install a rear view mirror in order to secure rearward visibility. Recently, as a rear view mirror attached to a vehicle interior (hereinafter, referred to as an “inside mirror”), an electronic mirror device has been proposed and practically used. The electronic mirror device includes a liquid crystal display for displaying a rear view of the vehicle, and can provide a vivid rear view to a driver in various travelling environments (for example, PTL 1). The electronic mirror device of this type includes a one-way mirror that reflects a part of incident light and transmits a part of the incident light, and a liquid crystal display disposed on a rear surface side of the one-way mirror. The one-way mirror reflects incident light from a front surface side (a side exposed to a driver), and transmits incident light from a rear surface side (a liquid crystal display side).
FIG. 1A and FIG. 1B are views illustrating typical use states of inside mirror 1A applied with the electronic mirror device. As illustrated in FIG. 1A and FIG. 1B, inside mirror 1A is attached near a ceiling in a vehicle interior. An attachment angle of inside mirror 1A is adjusted such that a driver can visually recognize a reflected image of rear view R projected on one-way mirror 11. Angle α formed by a front direction of inside mirror 1A and a sight line direction of the driver is referred to as “sight line angle α”. Sight line angle α takes a value within a range defined based on an eyellipse (a region representing a statistical distribution (eye range) of a position of an eye of the driver with an ellipse) for each vehicle type (for example, 2.85°≤α≤10.35°).
In inside mirror 1A, when liquid crystal display 12 is not turned on, the reflected image projected on one-way mirror 11 is visually recognized (refer to FIG. 1A). On the other hand, when liquid crystal display 12 is turned on, a display image of liquid crystal display 12 is visually recognized through one-way mirror 11 (refer to FIG. 1B). As illustrated in FIG. 1B, a sight line angle when rearward visual recognition is performed by using the display image of liquid crystal display 12 is referred to as “sight line angle β”.
FIG. 2 illustrates luminance characteristics of a conventional liquid crystal display. As illustrated in FIG. 2, in the conventional liquid crystal display, luminance of an image is maximized when a liquid crystal panel is viewed from a front direction, and an image in this state is visually recognized most easily. In the following description, a radiation angle of emitted light when luminance of an image is maximized is referred to as a “peak angle”, and is denoted by deviation angle ϕ in an up/down direction (vertical direction) with a case in which the liquid crystal panel is viewed from the front direction as a reference. Further, a direction in which luminance of the display image of the liquid crystal display is maximized is referred to as a “maximum luminance direction”. In other words, in the conventional liquid crystal display, peak angle ϕ is 0°, and the front direction is the maximum luminance direction.
Applying an optical member of a beam-converging type (for example, a reverse prism sheet) to a backlight of the liquid crystal display can enhance a luminance peak of the image when the liquid crystal panel is viewed from the front direction, thereby further improving visibility in the front direction in this case. The optical member of the beam-converging type is disclosed in PTL 2, for example.